Dynamically stabilized magnetic array

ABSTRACT

This application relates to devices and accessories that include or are configured to react with a mixture of electromagnets and permanent magnets. In particular the permanent magnets are configured to maintain persistent connections between components while the electromagnets are configured to pulse or activate periodically to maintain the connections or fix alignment of the various connections in certain circumstances.

FIELD

The described embodiments relate generally to magnetic attachmentfeatures. More particularly, the present embodiments relate toconfigurations in which magnetic attachment features are augmented withelectromagnets.

BACKGROUND

Attachment features formed with permanent magnets offer robust andconsistent attachment mechanisms for temporarily joining componentstogether. The use of permanent magnets is generally preferable to theuse of electromagnets because a permanent magnet does not require apower source. Unfortunately, because a size of the magnetic fieldemitted by the permanent magnets is fixed in strength and shape, astrength and or size of the magnetic field emitted by the permanentmagnets oftentimes must be minimized to avoid adverse interactionbetween the magnetic field and nearby magnetically sensitive objectsalong the lines of credit card magnetic strips. For this reason, aresulting attachment force may be sufficient to maintain the componentsjoined under normal conditions, but insufficient to keep the componentsjoined under peak or abnormal operating conditions. For example, anunintentional bump or jostling of the coupled components may apply aforce that decouples the joined components by overcoming the attachmentforce. Furthermore, even when a size or strength of the magnetic fieldis not constrained the magnetic coupling may not be strong enough towithstand certain operating conditions, because even rare earth elementpermanent magnets have a saturation point at which the magnetic fieldcannot be further increased.

SUMMARY

This paper describes various embodiments that relate to magneticattachment features.

An electronic device is disclosed that includes at least the followingelements: a power source; an electromagnet; a magnetic field sensor thatincludes a switch that electrically couples the electromagnet with thepower source to energize the electromagnet when changes detected by themagnetic field sensor in a magnetic field fall within a predefined rangeof magnetic field characteristics; and a device housing enclosing thepower source, the electromagnet and the magnetic field sensor.

A portable electronic device is disclosed and includes at least thefollowing elements: a power source; a number of electromagnetassemblies, each of the electromagnet assemblies including anelectromagnet, a magnetic field sensor and a switch, the switch allowingelectrical energy from the power source to energize the electromagnetwhen the magnetic field sensor detects a magnetic field falling within apredefined range of magnetic field characteristics; and a permanentmagnet configured to secure a magnetically attractable device to anexterior surface of the portable electronic device.

A portable computing device is disclosed and includes at least thefollowing: a housing formed of a non-ferrous material; a displayassembly disposed within the housing; a battery; and a number ofelectromagnet assemblies disposed within the housing, each of theelectromagnet assemblies comprising an analog switching mechanism thatsupplies power to an electromagnet from the battery when a sensing coildetects a changing magnetic field meeting a predefined magnetic fieldcharacteristic.

Other aspects and advantages of the invention will become apparent fromthe following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIGS. 1A-1E show various configurations in which two components arejoined using magnetic coupling features;

FIGS. 2A-2B show perspective and cross-sectional views of anelectromagnet;

FIGS. 2C-2D show circuit diagrams depicting how the magnetic fieldsensor can be configured;

FIGS. 3A-3B show various implementations of a tablet device that includesensor actuated electromagnets that can be configured to actuate upondetecting a magnetic field consistent with a stylus or span device;

FIG. 4A shows a configuration in which electromagnets of a device can beconfigured to interact with permanent magnets and/or magneticallyattractable material embedded within a protective case to reduce damageto the device in the event of a fall;

FIG. 4B shows how electromagnets can shift a device towards magneticallyattractable elements of protective case during the fall;

FIGS. 5A-5E depict a number of embodiments taking the form of variousinput devices;

FIG. 6 shows a flow chart illustrating a method for detecting changes ina magnetic field; and

FIG. 7 shows a block diagram of an electronic device suitable for usewith the described embodiments.

DETAILED DESCRIPTION

Representative applications of methods and apparatus according to thepresent application are described in this section. These examples arebeing provided solely to add context and aid in the understanding of thedescribed embodiments. It will thus be apparent to one skilled in theart that the described embodiments may be practiced without some or allof these specific details. In other instances, well known process stepshave not been described in detail in order to avoid unnecessarilyobscuring the described embodiments. Other applications are possible,such that the following examples should not be taken as limiting.

In the following detailed description, references are made to theaccompanying drawings, which form a part of the description and in whichare shown, by way of illustration, specific embodiments in accordancewith the described embodiments. Although these embodiments are describedin sufficient detail to enable one skilled in the art to practice thedescribed embodiments, it is understood that these examples are notlimiting; such that other embodiments may be used, and changes may bemade without departing from the spirit and scope of the describedembodiments.

High strength permanent magnets along the lines of rare earth elementmagnets, provide substantial, persistent magnetic fields at no powercost. Unfortunately, the fields produced by the permanent magnets arenot always ideal and cannot be adapted to fit every particularsituation. Unfortunately, in certain circumstances a field produced bythe permanent magnet may interfere with neighboring components ordevices. Furthermore, a magnetic coupling created by permanent magnetsmay not be strong enough to withstand certain challenging workingenvironments in which peak forces applied to the magnetic couplingexceed the forces provided by the magnetic attraction. Whileelectromagnets are capable of producing a substantially strongermagnetic field than even the highest strength permanent magnets and thatstrength can be modulated to suit various operating environments,electromagnets must be attached to a power source and steadily drainpower from that power source during operation of the electromagnet.

One way to overcome the aforementioned issues is to utilize a magneticattachment feature with both permanent magnets and electromagnets thatrelies primarily on the permanent magnets to maintain a persistentconnection between two or more components, while periodically utilizingthe electromagnets to augment the permanent magnets in certainsituations. In this way, a power expenditure required by theelectromagnets is minimized while the permanent magnets are augmented insituations in which the permanent magnets would otherwise beinsufficient. Such a configuration beneficially allows designers toreduce a size and strength of a persistent magnetic field emitted by thepermanent magnets without having to worry about disconnection of thecomponents. In some embodiments, actuation of the electromagnets can bebased upon a sensor that measures changes in the magnetic field emittedby the permanent magnets. Such a sensor can be configured to detect achange in the magnetic field resulting from initial movement of themagnets with respect to one another.

In one embodiment, the sensor for detecting relative movement betweenthe magnets can be embodied by a sensing coil in electricalcommunication with a field effect transistor (FET) switch. Because theFET switch is sensitive to changes in voltage induced in the sensingcoil by changes in a position of a nearby magnet field, the FET switchcan be configured to activate and deactivate in response to changes involtage that correspond to separation of two or more magneticallycoupled components. In some embodiments, internal circuitry of the FETswitch can be designed to actuate only in situations that correspond tounintentional separation events. For example, the FET switch can bedesigned to remain closed when a more gradual and small change involtage associated with a deliberate separation is detected. In thisway, the electromagnets can be actuated only when an inadvertentseparation is detected. Response time of the internal circuitry can beespecially timely when the FET is fully analog as the logic can all bebuilt into the circuitry of the switch without being slowed bycommunications delays generally associated with digital circuitry. Itshould be noted that sensing coil and FET switch embodiments are usedhereinafter for exemplary purposes only and should not be construed aslimiting as any switch capable of detecting changes in and/or shiftingof magnetic fields can utilized in lieu of the described FET switch. Forexample, in some embodiments the sensor can be embodied as a Hall-EffectSensor. Other mechanical sensing mechanisms are also possible. Forexample, a magnet disposed on the end of a leaf spring switch could alsobe employed.

In some embodiments, the FET switch can also be configured to improveways in which magnetically attractive components connect. For example,when a magnetic field associated with one component is first detected bythe FET switch, the electromagnet can be configured to actuate so that adistance at which a magnetic force begins to act upon and connect withthe component is increased. In other embodiments, the electromagnetscould be configured to receive power in an opposite direction whendisconnection of the components is desired. Such an outcome can bedesirable when for example the electromagnets are configured to retainthe components in all situations except when disconnection isspecifically requested by way of a user interface.

In some embodiments, the FET switch can be configured to balance out aresponse of a protective case during a drop event, when magnetic forcesgenerate a voltage change in the sensing coil that is indicative of adrop event. In other embodiments, other sensors such as an accelerometercan be utilized in cooperation with the FET switch to determine when thedrop event has occurred. In response to such a detection, theelectromagnets can be configured to emit a magnetic field that extendsportions of the case away from the electronic device so that uponcontacting a hard surface the electromagnets can at least partiallycontrol a rate at which the electronic device decelerates by creating agap between the electronic device and the case that effectively acts asa thicker case during impact. Additionally once the gap between theelectronic device and the case is closed the electromagnets couldreverse and aid in device retention during the rebound from the initialimpact. In this way, damage during the drop event can be prevented or atleast reduced.

These and other embodiments are discussed below with reference to FIGS.1A-7; however, those skilled in the art will readily appreciate that thedetailed description given herein with respect to these figures is forexplanatory purposes only and should not be construed as limiting.

FIGS. 1A-1E show various configurations in which two components can betemporarily joined using magnetic coupling features. In someembodiments, one or both of the components can be an electronic device.In some embodiments, the electronic device can take the form of asmartphone or tablet device having a non-ferrous or substantiallymagnetically neutral housing formed from a material along the lines ofan aluminum alloy that surrounds and protects the described components.The different configurations depicted include ones in which permanentmagnets and electromagnets are interspersed. FIG. 1A shows aconfiguration in which electromagnets 102 of both device 100 and 150 arepositioned on both ends of one side of each device. In some embodiments,electromagnets 102 can be activated by receiving energy from powersource 104 only when magnetic field sensors 106 detect a predeterminedmagnetic signature. In some embodiments, magnetic field sensors 106 canbe configured to recognize any one of a number of magnetic signatures.In this particular embodiment, magnetic field sensors 106 disposedwithin device 100 can be configured to recognize a changing magneticfield consistent with permanent magnets in a configuration similar topermanent magnets 108 of device 150 approaching device 100. Once themagnetic signature reaches a predetermined strength, magnetic fieldsensors 106 can be configured to engage a switch that allows energystored within power source 104 to energize electromagnets 102. Asdepicted, the dotted lines show how electromagnets 102 can be coupledwith power source 104 by way of magnetic field sensor 106. By includinga switching device in magnetic field sensor 106, magnetic field sensor106 can electrically couple electromagnets 102 with power source 104 byactuating the switching device as soon as a predefined stimulus isdetected by magnetic field sensor 106. It should be noted that thisconfiguration allows two devices such as devices 100 and 150 with thesame or substantially similar magnetic configurations to be joinedtogether. For example, FIG. 1A shows how devices 100 and 150 havesubstantially the same magnet configuration, meaning that by rotatingone of the items by 180 degrees the devices can be coupled together.FIG. 1A also shows how magnetic attraction forces 110 betweenelectromagnets 102 can be substantially greater than the magneticattraction force 112 between permanent magnets 108. Depending on anamount of energy supplied by power source 104, the forces provided byelectromagnets 102 can vary greatly. In some cases the force providedcan be less than that provided by the permanent magnets and in othercases the force provided by the electromagnets can be an order ofmagnitude greater than the force provided by the permanent magnets.

FIG. 1B shows a situation where a differential field strength can beconsidered when supplying power to electromagnets 102. For example, inthe depicted embodiment, readings from magnetic field sensor 106-1 wouldtend to be substantially greater than readings from magnetic fieldsensor 106-2. Without a comparator circuit 114, magnetic field sensor106-2 would tend to actuate its corresponding electromagnet 102 prior tomagnetic field sensor 106-1. By adding comparator circuit 114 to compareinputs received from each of magnetic field sensors 106-1 and 106-2,comparator 114 can cause actuation of electromagnet 102 by magneticfield sensor 106-2 to be delayed while actuation of electromagnet 102 bymagnetic field sensor 106-1 can be commanded without delay. In this way,the sides of devices 100 and 120 can be brought together in a muchflatter orientation. This type of orientation normalizing can bebeneficial when, for example, the devices are configured with connectorsthat require a particular orientation to couple together. In someembodiments, the nearer magnetic field sensor 106-2 can be configured tocommand its associated electromagnet 102 to exert a repulsive force whena difference between magnetic field sensors 106-1 and 106-2 isparticularly great. It should be noted that the variance ofelectromagnet output based upon differential magnetic field sensor datacan be applied to any of the described embodiments that include multiplemagnetic field sensors.

FIG. 1C shows a configuration in which electromagnets 102 are onlyincluded in electronic device 130 and accessory device 150 includes onlypermanent magnets and magnetically attractable material. In this way,accessory device 150 without the electromagnets need not include a powersource to actuate electromagnets. FIG. 1C also shows how sensors 106 canbe arranged at either end of device 170, allowing them to be separatedby a substantial distance. In this way, differential data received bycomparator 114 from sensors 106 can be accentuated. It should also benoted that electronic device 130 can have a symmetric magneticconfiguration, thereby allowing accessory device 150 to be attached toelectronic device 130 in at least two different orientations. FIG. 1Calso depicts a configuration in which accessory device 150 ismagnetically coupled with electronic device 130. When separation force152 is applied asymmetrically to one end of accessory device 150,electromagnet 102 can be energized by actuation of FET circuitryassociated with magnetic field sensor 106, thereby causing force 132 tobe generated at electromagnet 102. When force 152 is an abruptly appliedforce, force 132 generated by electromagnet 102 can be correspondinglyshort in duration to counter force 152. In some embodiments, when force152 is a long steady pull rather than an impulse, then the FET circuitrycan be configured to ignore an relatively slow changing magnetic fieldassociated with the steady pull.

FIG. 1D shows an additional alternative configuration in which magneticfield sensor 106 takes the form of a single FET switch and sensor coilcombination that is positioned in the middle of one side of electronicdevice 160 for detachment, detection and actuation operations executedby both electromagnets 102. In this way, fewer sensors need be includedin the design. Furthermore, the single FET switch configuration can beactuated in accordance with magnetic field readings received from asingle sensor so the data need not be cross-checked. In someembodiments, a more complex FET switch can be used that can characterizean orientation of the magnetic field emitted by electronic device 170.In this way, varied actuation of electromagnets 102 can still becommanded based on a determined orientation of a magnetic field emittedby electronic device 180. In some embodiments, a magnetic sensor 172associated with electronic device 170 can be configured differently thanthe magnetic field sensor of electronic device 170. For example,actuation of electromagnets 102 of electronic device 170 can be delayeduntil actuations of electromagnets 102 of electronic device 160 aredetected by magnetic field sensor 172. In this way a more complex,higher cost magnetic field sensor 106 can be included in a primarydevice while a lower cost magnetic field sensor 172 can be included inelectronic device 170.

FIG. 1E shows an additional embodiment in which electronic device 180includes power source 104 while electronic device 190 does not. In thisembodiment power source 104 is configured to supply power toelectromagnets in both electronic device 180 and 190. Dotted linesrunning from magnetic field sensor 106 show how energy from power source104 can be routed between the devices. The inter-device energy transfercan be enabled in any of a number of ways including, for example bydiscrete electrical connectors or in some cases by inductive energytransfer. While reliance upon power source 104 of electronic device 180for energizing of electromagnets 102 of electronic device 190 can limitthe number of situations in which electromagnets 102 of electronicdevice 190 can be employed, those electromagnets are still formed ofmagnetically attractable materials which can interact with attractionfields emitted by magnets within electronic device 180. Whileelectromagnets are shown in both devices it should be understood that insome embodiments, electronic device 180 may include no electromagnets atall and can rely completely upon energizing of electromagnets 102 ofelectronic device 190.

FIGS. 2A-2C show perspective and cross-sectional views of one ofelectromagnets 102. In particular, FIG. 2A shows a perspective view ofelectromagnet 102. As depicted, electromagnet 102 is formed from amagnetically attractable substrate 202 substantially wrapped withincoils 204. Coils 204 can be formed of wires having a wire diameter ofbetween 0.06 mm and 0.25 mm and in some embodiments have an average winddiameter of about 5 mm. Actuation of coils 204 by a power source cancreate a magnetic field that creates field lines extending throughmagnetically attractable substrate 202. In some embodiments,magnetically attractable substrate 202 can include any one of a numberof metals including stainless steel and mu metal arranged in any numberof shapes. The figures depict magnetically attractable substrate 202 ashaving a u-shaped geometry. In some embodiments, magneticallyattractable substrate 202 can be a magnetized magnetic substrate alongthe lines of rare earth metal magnets or ferromagnetic compounds. Amagnetic substrate has the advantage of providing a persistent magneticfield even without receiving current; however, in certain cases astainless steel or mu metal substrate can generate a much largermagnetic field than a magnetic substrate since the magnetic fieldsaturation level for mu metal and stainless steel is substantiallyhigher than saturation levels for magnetic substrates. When coils 204receive electrical energy in the form of electrical current a magneticfield can be emitted. Magnetically attractable substrate 202 issurrounded by coils 204 so that when current is routed through coils204, magnetically attractable substrate 202 acts to help magnify themagnetic field generated by coils 204. In some embodiments, the coilscan be configured as depicted maintaining about the same thickness ofwires and broadening as magnetically attractable substrate 202 broadensnear a base of electromagnet 102. Electromagnet 102 also includeselements 206 that can be configured to help insulate magneticallyattractable substrate 202 and a magnetic field it conducts from othernearby magnetically sensitive components.

FIG. 2B shows a cross-sectional view of electromagnet 102 and howmagnetically attractable substrate 202 can direct a magnetic fieldrepresented by field lines 208 through electromagnet 102. In this way, amagnetic field in region 210 can be oriented in a direction opposite toregion 212. FIG. 2B also shows how electromagnet 102 is in electricalcommunication with magnetic field sensor 106. In some embodiments, FETcircuitry of magnetic field sensor 106 can be arranged so that a rate atwhich magnetic field induced voltage changes within the FET circuitrycorresponds to whether or not the switching mechanism of the FETcircuitry is actuated. For example, in some embodiments, FET Circuitryof magnetic field sensor 106 is configured to respond to a change involtage induced by shifting of magnetic fields in various ways. In oneconfiguration, the FET circuitry of magnetic field sensor 106 can beconfigured to filter out magnetic field changes consistent with a slowcontinuous force applied to an accessory device. In such a configurationthe FET circuitry can be arranged to actuate electromagnets 102 when achanging magnetic field is detected that is consistent with a quick pullor jostle imparted to the accessory device. In this way a rapidenergizing of electromagnet 102 sufficient to prevent separation of theaccessory device can be commanded, while an intentional removalconsistent with the continuous pull on the accessory device can beaccomplished without energizing electromagnets 102. For example, such aconfiguration can be useful when operating an electronic device on amoving platform such as a commuter bus or train. When the movingplatform travels over a bump or switches tracks, resulting transitoryforces applied to the device and accessory can be opposed by rapidactuation of electromagnets 102. Unfortunately, in certain circumstancesthis type of configuration can allow disconnection of the accessorydevice when unintentional persistent forces are applied. Such adisconnection may be preferable to a system that would actuateelectromagnets 102 over a long period of time to oppose theunintentional persistent force because persistent actuation ofelectromagnets 102 can unduly drain a battery of the device to which theaccessory device is magnetically coupled.

FIG. 2C shows an exemplary layout of an analog FET circuit switchsuitable for use with the described embodiments. Variation in resistanceand capacitance of the depicted elements can help to tune a response ofFET Circuitry of the Control FET to changes in voltage experiencedacross a sensing coil taking the form of magnetic field sensor 106caused by shifting magnetic fields. In some embodiments, the depictedFET circuitry can act as a band pass filter that both helps the FETcircuit avoid false triggers and limits the duty cycle so an expenditureof power to the magnets can be limited so as to not unduly reducebattery life of the device with which the electromagnet is associated.It should be noted that the band pass filter is not a requirement fordriving a FET circuit with a sensing coil, and in certain applications adirect connection between magnetic field sensor It should be noted thatwhile FIG. 2C shows a fully analog circuit, other digital circuitry canbe included. For example, in some embodiments an additional switch canbe incorporated that routes power to electromagnet 102 based uponsignals passed digitally. Such a configuration can be beneficial whenactuation of electromagnet 102 is based upon additional sensors providedby digital circuits, the output of which can be combined and analyzed bya processor for determination of whether or how much to energize any oneof electromagnets 102. In some embodiments, the other switchconfigurations can include inputs from a magnetometer or accelerometerof an associated device.

FIG. 2D shows an alternative layout for the switch circuitry. Inparticular FIG. 2D shows a simplified layout in which magnetic fieldsensor 106 and electromagnet 102 are combined and the band pass filteris omitted. Magnetic field sensor 106 can be included with electromagnet102 by configuring the coils that energize electromagnet 102 as asensing coil. In this way, voltage changes in the electromagnet coilcaused by changing or shifting magnetic fields can be utilized toactuate and deactivate the FET switch. Alternatively, electromagnet 102can include a second set of coils wrapped around it that are configuredto measure voltage changes resulting from magnetic field changes. Thisconfiguration effectively allows electromagnet 102 to both sense andgenerate magnetic fields.

FIGS. 3A-3B show various implementations of a tablet device that includesensor actuated electromagnets that can be configured to actuate upondetecting a magnetic field consistent with a stylus or span device. FIG.3A shows stylus 302 having permanent magnet arrays 304 and 306 affixedto one side of tablet 300. In some embodiments, an orientation sensorwithin stylus 302 can be utilized to maintain an orientation of stylus302 consistent with an orientation of tablet 300 by varying magneticfields emitted by electromagnets within stylus 302 or by modulatingmagnetic fields emitted by electromagnets 102 disposed within tablet300. This type of system can be embodied in any number of ways. Forexample, in some embodiments, when stylus 302 and tablet 300 are incommunication by way of a wired or wireless connection (such as aBluetooth® connection) orientation sensors in both the tablet and thestylus can be compared to determine whether alignment of stylus 302 isrequired. When misalignment is detected electromagnets 102 can emit aquick pulse that guides magnets within stylus 302 into a predefinedposition. Alternatively the quick pulsing can be periodically emittedwhenever a stylus is in wireless communication with tablet 300. In someembodiments, this can maintain stylus 302 in a substantially parallelorientation with respect to a surface of tablet 300. In someembodiments, tablet 300 can be configured to activate electromagnets 102to initiate connection or disconnection of stylus 302. While notspecifically depicted, tablet 300 can include permanent magnets formaintaining stylus 302 against an outer surface of tablet 300. In thisway, electromagnets need not stay energized to retain stylus 302 incontact with tablet 300.

FIG. 3B shows another optimization of a magnetic connection for a stylusor span connector in which an orientation of the stylus or span devicecan be corrected to align with an associated electronic device. In someembodiments, tablet 310 can include magnetic flux detection sensorsconfigured to activate electromagnets 102 upon a magnetic fieldassociated with span 312 emitting a magnetic flux having a minimumpredetermined magnetic flux. The minimum magnetic flux level can beconsistent with a distance at which electromagnets 102 can quickly drawspan 312 towards tablet 310.

FIG. 4A shows an implementation in which electromagnets 102 of a device400 can be configured to interact with permanent magnets and/ormagnetically attractable material embedded within a protective case 410to reduce damage to the device in the event of a fall. Sensors of device400 along the lines of accelerometers and/or gyroscopes can beconfigured to determine any time device 400 is in free fall. When device400 is able to determine a most likely point of impact a position ofdevice 400 within protective case 410 can be adjusted by activatingselect ones of electromagnets 102. The magnetically attractable materialof protective case 410 can include magnetically attractable ormagnetized material. In some embodiments, the magnetically attractablematerial can include a flexible steel shell that can be manipulated byelectromagnets 102 of device 400 so that a distance between corner 412of protective case 410 and device 400 can be maximized by engagingelectromagnets 102-1 and 102-2 of device 400 to maneuver device 400towards a top-most corner of protective case 410 as depicted in FIG. 3D.In some embodiments instead of forming all of protective case 410 ofmagnetically attractable material only discrete elements 414 can bemagnetically attractable or magnetic.

FIG. 4B shows how electromagnets 102-1 and 102-2 bias device 400 towardsmagnetically attractable elements 414 of protective case 410. Oncecorner 412 of protective case 410 impacts a hard surface the spacebetween protective case 410 and device 400 forms a crush zone thatreduces a rate at which force from the impact is imparted to device 400,thereby reducing a likelihood of damage. In some embodiments, powersupplied to electromagnets 102-1 and 102-2 can be slowly reduced tofurther be controlled. This can be particularly effective once theestablished crush zone has flattened and no longer has any give left asit can allow even greater control over a rate of deceleration. FETswitches within device 400 can be utilized to determine when movement ofdevice 400 with respect to protective case 410 exceeds a predeterminedthreshold. Such a detection even by the FET switches can be used toadjust motion of device 400 with respect to protective case 410 byactivating select electromagnets 102. It should be noted that while anembodiment in which a corner impacts a solid surface is depicted thedescribed embodiments can also be applied in drop event situations wheresubstantially all of one side of protective case 410 impacts a hardsurface. Furthermore, in certain embodiments, a FET switch along thelines of those previously described can be used to determine if device400 is in the process of being disengaged from protective case 410 bymonitoring voltage changes within a sensing coil with which the FETswitch is in electrical contact. In such a case, all or an appropriatenumber of electromagnets 102 can be pulsed to retain device 400 withinprotective case 410.

FIGS. 5A-5D depict a number of embodiments taking the form of variousinput devices in accordance with the described embodiments. Inparticular, an input device 500 configured to provide visual and tactilefeedback to a user is depicted. Input device 500 can provide visualfeedback by way of a flexible display 502 secured to a top surface oftop layer 504 of input device 500. FIG. 5A also shows internal elementswithin input device 500 by removing a flexible covering that wouldotherwise mask the edges of input device 500. As depicted, an array ofmagnetic elements 506 are shown dispersed along an interior facingsurface of bottom layer 508 of input device 500 while another array ofmagnetic elements 510 are dispersed across an interior facing surface oftop layer 504. FIG. 5A shows a configuration in which the arrays ofmagnetic elements 506 and 510 are arrays of permanent magnets that havealternating polarities configured to exert repulsive magnetic fieldsthat force substantially all of top layer 504 of input device 500 into asubstantially planar configuration. FIG. 5A also depicts an array ofelectromagnets 512 embedded within bottom layer 508. Electromagnets 512can be configured to produce an attractive field substantially largerthan the repulsive field so that after a portion of top layer 504 hasbeen depressed by a predefined amount, the electromagnet then energizesand draws an associated magnetic element 510 into contact or closeproximity to an associated magnetic element 506. Electromagnet 512 canbe equipped with a discrete magnetic field sensor along the lines of aFET switch as described above to determine when the particular distancehas been reached. In some embodiments, a reduction in size can beachieved by integrating a sensing coil associated with the FET switchinto an associated electromagnet 512. In this way, positive feedback canbe provided to assure a user that an input has been detected. It shouldbe noted that in some embodiments, arrays of magnetic elements 506 and510 can be arranged in a configuration that allows top layer 504 to becompressed against bottom layer 508 by shifting top layer 504 or bottomlayer 508 laterally to align the various magnetic elements. In this way,attractive forces are generated drawing the two layers together to forma low-Z form factor input device 500 that can be easily stored orotherwise positioned when not in use.

FIG. 5B shows how flexible display 502 can be configured to indicatevarious areas of top layer 504 that define user inputs. When a touch isdetected by a touch sensor of display 502 within one of the indicatedareas, such as one of areas 514, 516 or 518, magnetic elements 506 and510 lying beneath the indicated area in which the touch is detected canbe coupled together, so that when one of magnetic elements 510 iscompressed electromagnets 512 drive the other magnetic elements 510 tofollow the magnetic element receiving the force. Area 518 is depicted inan actuated state in which multiple magnetic elements 510 move togetherto provide the appearance of a large key being temporarily depressed inresponse to a user input. While a generic pattern of buttons is depictedit should be understood that any desired pattern of keys can be definedby flexible display 502 and the magnetic element arrays.

FIGS. 5C and 5D show an alternative input device 550 that includeselectromagnets on at least an interior facing surface of a bottom layerof input device 550 that cooperate with permanent magnets attached to atop layer of input device 550 to control contours of input device 550.The electromagnets within input device 550 can be selectively actuatedto define various control schemes. FIG. 5C shows an exemplary controlscheme in which protrusions formed by commanding certain combinations ofthe electromagnets to be energized. In some embodiments, each key cancorrespond to a discrete electromagnet and permanent magnet exertingopposing magnetic fields upon one another. Input device 550 can bewrapped in many different materials such as plastic, fabric or evenmicrofiber. In some embodiments, a single key can be formed of multiplepairs of magnetic elements 506 and 510. In this way, a larger key havinga customized shape can be created. In some embodiments, a tactileresponse of each key can be driven entirely by an amount of currentsupplied to each electromagnet. FIG. 5C also shows how display 502 canbe configured to provide information about various ones of the keys ascan be seen by key descriptions 1 and 2. In some embodiments, display502 can also include illustration 1 as depicted. Illustration 1 caninclude any decorative or functional imagery having any amount ofutilitarian or cosmetic value. Each of keys 552 can be configured toprovide tactile feedback to a user when the user exerts a force on aparticular key 552. For example, in some embodiments a click feel can bedesired in which resistance is initially great and then the resistanceis reduced to allow the key to descend before it returns to its formerposition. In some embodiments, each key can be configured to respond ina particular way in all circumstances, while in other embodiments,feedback response can be varied depending on a chosen application oruser interface layout.

For example, in some embodiments, input device 400 can be configured todisplay a piano style keyboard interface as depicted in FIG. 5D. In apiano configuration, the keyboard would be made up of two types of keys,black keys 554 and white keys 556. In some embodiments, only black keys554 can be elevated while white keys 556 are defined only by visual cuesprovided by display 502. In some embodiments, white keys 556 can beelevated only half as much as black keys 554, so that tactile feedbackcan be provided for each key of the keyboard. In some embodiments,corresponding combinations of electromagnets and permanent magnets canbe larger or smaller depending upon an amount of resolution desired whendefining three-dimensional shapes upon input device 550. While a pianolayout is depicted other embodiments are also possible such as forexample a drum layout or in some cases a standard keyboard layout.

FIG. 5E shows various feedback response profiles that can be commandedin accordance with the described embodiments. Feedback response profile560 can appropriate for use with the button embodiments described inFIGS. 5A-5C. Repulsion by magnetic fields creates an initial increase inresistance; however once a certain amount of displacement is achieved anelectromagnet is actuated which draws the keyboard down for a verysatisfying user indication that the keystroke has been received. Thedescribed embodiments can provide superior feedback response on theorder of a 1:1 feedback ratio, because unlike a more traditional domeswitch, the slope of the curve once sufficient force has been appliedcan be extremely steep, as depicted by response profile 560. Byproviding such a definite feedback response an amount of travel of eachkey or button can be reduced without preventing a user from receivingunmistakable feedback of key or button actuation. FIG. 5E also showsresponse profile 570. This response profile might be appropriate for usewith a variable feedback key such as the piano keyboard depicted in FIG.5D. The slow ramp up in pressure to depress the key can be consistentwith a real piano. It should be noted that the response profiles shouldnot be construed as limiting and that electromagnet driven buttons andkeys can assume many different profiles to match many different userinterface configurations. In some embodiments, a device attached toinput device 500 or 550 can be configured to transmit a different userinterface scheme and control feedback for any one of a number ofapplications.

FIG. 6 shows a flow chart illustrating a method 600 for detecting andreacting to a changing or shifting magnetic fields. At step 602 achanging magnetic field is detected. The changing magnetic field can bedetected in many ways, but in one embodiment a sensing coil combinedwith a FET switch can be used to detect and react to changes in magneticfields. Circuitry within the FET switch can be adjusted to filter outcertain types of magnetic field changes. At step 604, when the changingmagnetic field matches a predefined magnetic field profile a switch isengaged. At step 606, engagement of the switch energizes anelectromagnet. The energized electromagnet can be configured to performmany tasks including preventing disconnection of an accessory from adevice, initializing a connection between two devices, or even providinga tactile response to a user input to a name a few. At step 608, whenthe changing magnetic field no longer matches the predefined magneticfield profile the electromagnet is de-energized.

FIG. 7 is a block diagram of an electronic device 700 suitable for usewith the described embodiments. The electronic device 700 illustratescircuitry of a representative computing device. The electronic device700 includes a processor 702 that pertains to a microprocessor orcontroller for controlling the overall operation of the electronicdevice 700. The electronic device 700 stores media data pertaining tomedia items in a file system 704 and a cache 706. The file system 704is, typically, a storage disk or a plurality of disks. The file system704 typically provides high capacity storage capability for theelectronic device 700. However, since the access time to the file system704 is relatively slow, the electronic device 700 can also include acache 706. The cache 706 is, for example, Random-Access Memory (RAM)provided by semiconductor memory. The relative access time to the cache706 is substantially shorter than for the file system 704. However, thecache 706 does not have the large storage capacity of the file system704. Further, the file system 704, when active, consumes more power thandoes the cache 706. The power consumption is often a concern when theelectronic device 700 is a portable media device that is powered by abattery 708. The electronic device 700 can also include RAM 710 andRead-Only Memory (ROM) 712. The ROM 712 can store programs, utilities orprocesses to be executed in a non-volatile manner. The RAM 710 providesvolatile data storage, such as for the cache 706.

The electronic device 700 also includes a user input device 714 thatallows a user of the electronic device 700 to interact with theelectronic device 700. For example, the user input device 714 can take avariety of forms, such as a button, keypad, dial, touch screen, audioinput interface, visual/image capture input interface, input in the formof sensor data, etc. Still further, the electronic device 700 includes adisplay 716 (screen display) that can be controlled by the processor 702to display information to the user. A data bus 718 can facilitate datatransfer between at least the file system 704, the cache 706, theprocessor 702, and the CODEC 720.

In one embodiment, the electronic device 700 serves to store a pluralityof media items (e.g., songs, podcasts, etc.) in the file system 704.When a user desires to have the electronic device play a particularmedia item, a list of available media items is displayed on the display716. Then, using the user input device 714, a user can select one of theavailable media items. The processor 702, upon receiving a selection ofa particular media item, supplies the media data (e.g., audio file) forthe particular media item to a coder/decoder (CODEC) 720. The CODEC 720then produces analog output signals for a speaker 722. The speaker 722can be a speaker internal to the electronic device 700 or external tothe electronic device 700. For example, headphones or earphones thatconnect to the electronic device 700 would be considered an externalspeaker.

The electronic device 700 also includes a network/bus interface 724 thatcouples to a data link 726. The data link 726 allows the electronicdevice 700 to communicate with a host computer or to accessory devices.The data link 726 can be provided over a wired connection or a wirelessconnection. In the case of a wireless connection, the network/businterface 724 can include a wireless transceiver. The media items (mediaassets) can pertain to one or more different types of media content. Inone embodiment, the media items are audio tracks (e.g., songs, audiobooks, and podcasts). In another embodiment, the media items are images(e.g., photos). However, in other embodiments, the media items can beany combination of audio, graphical or visual content. Sensor 728 cantake the form of circuitry for detecting any number of stimuli. Forexample, sensor 728 can include a Hall Effect sensor responsive toexternal magnetic field, an audio sensor, a light sensor such as aphotometer, and so on.

The various aspects, embodiments, implementations or features of thedescribed embodiments can be used separately or in any combination.Various aspects of the described embodiments can be implemented bysoftware, hardware or a combination of hardware and software. Thedescribed embodiments can also be embodied as computer readable code ona computer readable medium for controlling manufacturing operations oras computer readable code on a computer readable medium for controllinga manufacturing line. The computer readable medium is any data storagedevice that can store data that can thereafter be read by a computersystem. Examples of the computer readable medium include read-onlymemory, random-access memory, CD-ROMs, HDDs, DVDs, magnetic tape, andoptical data storage devices. The computer readable medium can also bedistributed over network-coupled computer systems so that the computerreadable code is stored and executed in a distributed fashion.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of specific embodimentsare presented for purposes of illustration and description. They are notintended to be exhaustive or to limit the described embodiments to theprecise forms disclosed. It will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

What is claimed is:
 1. An electronic device attachment system forattaching a releasable accessory device to an electronic device,comprising: a power source; a permanent magnet that produces a magneticfield that retains the accessory device to the electronic device; anelectromagnet switchably coupled to the power source, the electromagnethaving a magnetic force strength based on an amount of energy suppliedby the power source; and a magnetic field sensor capable of detectingchanges in the magnetic field, wherein when the magnetic field sensordetects a change in the magnetic field corresponding to a separationevent, energy is provided from the power source to the electromagnetsuch that the electromagnet is activated to prevent separation of theelectronic device and the accessory device.
 2. The electronic deviceattachment system as recited in claim 1, further comprising: a housingenclosing the power source, the electromagnet and the magnetic fieldsensor.
 3. The electronic device attachment system as recited in claim1, wherein the magnetic field sensor is a first magnetic field sensor,the electromagnet is a first electromagnet and wherein the electronicdevice further comprises: a second electromagnet switchably coupled tothe power source; a second magnetic field sensor that electricallycouples the second electromagnet with the power source; and a comparatorthat determines a difference between the magnetic field changes detectedby the first and second magnetic field sensors, wherein the comparatorprovides a signal that directs the first and second magnetic fieldsensors to independently activate the first and second electromagnets.4. The electronic device attachment system as recited in claim 1,wherein the electromagnet includes switching circuitry configured toreverse a direction current flows through coils of the electromagnet. 5.The electronic device attachment system as recited in claim 1, furthercomprising a user interface, wherein a processor in communication withthe user interface sends a signal directing release of the accessorydevice when a user input is received by the user interface requestingdisconnection of the accessory device from the electronic device.
 6. Theelectronic device attachment system as recited in claim 5, wherein theuser interface comprises a touch sensitive display assembly and thepower source comprises a battery.
 7. The electronic device attachmentsystem as recited in claim 1, wherein the accessory device is aprotective cover that is magnetically coupled with the electronic deviceby way of the permanent magnet.
 8. A portable electronic device,comprising: a power source; a number of electromagnet assemblies, eachof the electromagnet assemblies comprising an electromagnet, a magneticfield sensor and a switch, the switch allowing electrical energy fromthe power source to energize the electromagnet when the magnetic fieldsensor detects a magnetic field falling within a predefined range ofmagnetic field characteristics; and a permanent magnet configured tosecure a magnetically attractable device to an exterior surface of theportable electronic device.
 9. The portable electronic device as recitedin claim 8, further comprising: a comparator that compares magneticfield readings detected by each of the magnetic field sensors andadjusts the predefined range of magnetic field characteristics inaccordance with the magnetic field readings.
 10. The portable electronicdevice as recited in claim 9, further comprising a number of permanentmagnets arranged in an alternating polarity pattern complementary to apolarity pattern formed by permanent magnets of the magneticallyattractable device.
 11. The portable electronic device as recited inclaim 9, wherein the comparator adjusts the predefined range of magneticfield characteristics so that a first one of the electromagnets isenergized before a second one of the electromagnets.
 12. The portableelectronic device as recited in claim 11, wherein a sequentialenergizing of the electromagnets is performed at an interval that causesmating surfaces of the portable electronic device and the magneticallyattractable device to be aligned when the mating surface of the portableelectronic device and the magnetically attractable device first comeinto contact.
 13. The portable electronic device as recited in claim 12,wherein the magnetically attractable device is the same as the portableelectronic device.
 14. The portable electronic device as recited inclaim 8, wherein the electromagnet comprises two sets of coils arrangedabout opposing ends of a substantially u-shaped magnetically attractablematerial, the electromagnet emitting adjacent opposite polarity fields.15. The portable electronic device as recited in claim 8, furthercomprising a processor configured to direct a flow of energy through atleast one of the electromagnets to be reversed.
 16. A portable computingdevice, comprising: a housing formed of a magnetically neutral material;a display assembly disposed within the housing; a battery; and a numberof electromagnet assemblies disposed within the housing, each of theelectromagnet assemblies comprising an analog switching mechanism thatsupplies power to an electromagnet from the battery when a sensing coildetects a changing magnetic field meeting a predefined magnetic fieldcharacteristic.
 17. The portable computing device as recited in claim16, wherein the analog switching mechanism comprises a field effecttransistor switch.
 18. The portable computing device as recited in claim17, wherein the field effect transistor switch comprises a band passfilter that determines whether the predefined magnetic fieldcharacteristic is met and limits a duty cycle of the electromagnet.